1. Field of the Invention
The present invention relates to an automatic transmission having its gear train composed of a plurality of planetary gear sets and capable of changing the connection relations of the rotary components and, more particularly, to a shift control system for the automatic transmission, which is constructed to leave any of the planetary gear sets taking no part in the transmission of a power at a predetermined gear stage.
2. Description of the Related Art
As is well known, the gear train of an automatic transmission is composed of a plurality of planetary gear sets. This is partly because the planetary gear sets can be arrayed on line and made compact and partly because the meshing relations of the gears need not be changed to provide an excellent durability. The number of gear stages to be set by the automatic transmission of this kind naturally becomes larger for the larger number of the planetary gear sets used. In addition, however, the number of gear stages to be set can also be increased if the mutual connection relations of the rotary members--the sun gears, the ring gears and the carriers--of the planetary gear sets can be changed by clutch means. The automatic transmission having this structure is disclosed in Japanese Patent Laid-Open No. 60-57036, for example. We proposed in Japanese Patent Application No. Hei 1-185151 a gear shift mechanism for an automatic transmission, which uses planetary gear sets equal in number to that of Japanese Patent Laid-Open No. 60-57036 but has a larger number of gear stages to be set and can execute more various shift controls and improve the power performance.
One example of the system according to our proposal is shown in FIG. 6. First to third planetary gear sets 1, 2 and 3 are arrayed on a line between an in put shaft 4 and an output shaft 5. Each of these planetary gear sets 1, 2 and 3 has its rotary components, the input shaft 4 and the output shaft 5 are connected in the following manner. The carrier 1C of the first planetary gear set 1 is integrally connected to the ring gear 3R of the third planetary gear set 3. The ring gear 2R of the second planetary gear set 2 is integrally connected to the carrier 3C of the third planetary gear set 3, which is connected to the output shaft 5. There are also provided three sets of clutch means for connecting the individual rotary components of the planetary gear sets 1, 2 and 3 selectively to each other. Specifically, these three sets of clutch means are: second clutch means K2 for selectively connecting the sun gear 1S of the first planetary gear set 1 and the carrier 2C of the second planetary gear set 2; fourth clutch means K4 for selectively connecting the sun gear 1S of the first planetary gear set 1 and the sun gear 2S of the second planetary gear set 2; and fifth clutch means K5 for selectively connecting the carrier 2C of the second planetary gear set 2 and the sun gear 3S of the third planetary gear set 3. Of these, the fourth clutch means K4 is composed of a one-way clutch 20 and a multiple disc clutch 22 which are in parallel relation to each other.
In addition to these clutch means, there are also provided two clutch means: first clutch means K1 for selectively connecting the input shaft 4 and the ring gear 1R of the first planetary gear set 1; and third clutch means K3 for selectively connecting the input shaft 4 and the sun gear 1S of the first planetary gear set 1.
As the brake means, on the other hand, there are provided three sets of brake means: first brake means B1 for holding the sun gear 3S of the third planetary gear set 3 selectively in an immovable state; second brake means B2 for holding the carrier 2C of the second planetary gear set 2 selectively in an immovable state; and third brake means B3 for holding the sun gear 2S of the second planetary gear set 2 selectively in an immovable state. Of these: the first brake means B1 is composed of a one-way clutch 40 and a band brake 42 which are in parallel relation to each other; the second brake means B2 is composed of a one-way clutch 60 and a multiple disc clutch 61 which are in parallel relation to each other; and the third brake means B3 is composed of a band brake.
Incidentally, reference numeral 6 appearing in FIG. 6 designates a transmission casing (as will be shortly referred to as the "casing").
According to the system shown in FIG. 6, the connection relations between the rotary components of the individual planetary gear sets 1, 2 and 3 can be interchanged to set a number of gear stages. In addition, there are a plurality of kinds of engagement/release patterns for the clutch means and the brake means to set a predetermined one of the gear stages, as will be tabulated in the clutch and brake application chart of Table 1. Incidentally, in Table 1: symbols .largecircle. indicate the engaged stage; blanks indicate the released state; and symbols indicate that the corresponding means may be engaged. In addition, the means indicated by the symbol for the fifth clutch means K5 or the first brake means B1 at the 1st speed stage have one of the following characteristics: (1) the gear ratio and the revolving state remain unchanged even when it is released, (2) the revolving state but not the gear ratio is changed when released, and (3) the gear ratio and the revolving state remain unchanged even when released, if another means indicated by the symbol is engaged. In Table 1, moreover, the columns designated at a, b, c, - - - , and so on at the 2nd, 3rd, 4th and 5th speeds and in the reverse range indicate that the engagement/release pattern for setting the gear stage under consideration has a different rotational speed of the rotary components of the planetary gear sets. Still moreover, the numerals 1, 2, 3 - - -and so on indicate the kinds of the engagement/release patterns in which the rotational speeds of the rotary components of the planetary gear sets are not different.
TABLE 1 ______________________________________ Clutch Means Brake Means K1 K2 K3 K4 K5 B1 B2 B3 ______________________________________ 1st 1 .largecircle. .largecircle. .largecircle. .largecircle. * 2 .largecircle. .largecircle. .largecircle. * .largecircle. 3 .largecircle. .largecircle. * .largecircle. .largecircle. 2nd a 1 .largecircle. .largecircle. .largecircle. .largecircle. * 2 .largecircle. .largecircle. .largecircle. * .largecircle. 3 .largecircle. .largecircle. * .largecircle. .largecircle. b .largecircle. .largecircle. .largecircle. .largecircle. 2.2th .largecircle. .largecircle. .largecircle. .largecircle. 2.5th .largecircle. .largecircle. .largecircle. .largecircle. 2.7th .largecircle. .largecircle. .largecircle. .largecircle. 3rd a 1 .largecircle. .largecircle. * .largecircle. * 2 .largecircle. .largecircle. .largecircle. * .largecircle. b .largecircle. .largecircle. .largecircle. * c .largecircle. .largecircle. * .largecircle. d .largecircle. * .largecircle. .largecircle. 3.2th .largecircle. .largecircle. .largecircle. .largecircle. 3.5th .largecircle. .largecircle. .largecircle. .largecircle. 4th a 1 * .largecircle. .largecircle. .largecircle. * 2 .largecircle. .largecircle. .largecircle. * .largecircle. 3 .largecircle. .largecircle. * .largecircle. .largecircle. 4 .largecircle. * .largecircle. .largecircle. .largecircle. b .largecircle. .largecircle. .largecircle. * 5th a .largecircle. .largecircle. * .largecircle. b * .largecircle. .largecircle. .largecircle. c .largecircle. .largecircle. * .largecircle. Rev a 1 .largecircle. .largecircle. * * .largecircle. 2 .largecircle. .largecircle. .largecircle. .largecircle. * b * .largecircle. .largecircle. .largecircle. ______________________________________
Table 1 exemplifies the gear stages which can be set in principle. For practical use, one excellent in the power performance and the accelerability is selected from those gear stages. Specifically, a gear stage for providing a gear ratio having a relation approximate to the geometric series is selected as a major one, and one advantageous in the shift controllability and the durability is selected in Table 1 from the engagement/release patterns for setting the individual gear stages. In the structure shown in FIG. 6, on the other hand, the fourth clutch means K4, the first brake means B1 and the second brake means B2 use the one-way clutches 20, 40 and 60 in combination. In case, therefore, it is intended to block the revolution in the direction to release those one-way clutches 20, 40 and 60, the multiple disc clutch 22, the band brake 42 or the multiple disc clutch 61, all of which are in parallel relation to the former clutches, are engaged to bring their corresponding clutch means K4 and brake means B1 and B2 into their engaged states.
The setting of the gear stages in the system, as shown in FIG. 6, is executed while considering the power performance of the shift controllability, as has been described hereinbefore. For example, the 2nd speed is set according to the pattern of column b of Table 1, and the 3rd speed is set according to the pattern of column b or c. Considering the shift from the 3rd to 4th speed, the 3rd speed is set according to the pattern of column c. In this case, the 2nd speed is set by engaging the first clutch means K1, the fourth clutch means K4, the first brake means B1 and the third brake means B3. In the first planetary gear set 1, therefore, the ring gear 1R is rotated with the input shaft 4 with the sun gear 1S being held immovable. In the third planetary gear set 3, on the other hand, the sun gear 3S is held immovable, and the ring gear 3R is rotated at a speed which is decelerated from that of the revolutions of the input shaft 4 by the first planetary gear set 1. In the second planetary gear set 2, moreover, the sun gear 2S is held immovable, but the ring gear 2R is rotated together with the carrier 3C of the third planetary gear set 3. As a result, the individual rotary components of the planetary gear sets 1, 2 and 3 are mechanically caused to perform the specified motions by the closed chain. According to the pattern of column b or c of the 3rd speed, on the other hand, at least the first clutch means K1, the third clutch means K3 and the first brake means B1 are engaged. As a result, the first planetary gear set 1 has its sun gear 1S and ring gear 1R rotated together integrally with the input shaft 4 so that it is integrally rotated in its entirety. In the third planetary gear set 3, on the other hand, the ring gear 3R connected to the carrier 1C of the first planetary gear set 1 is rotated at the same speed as that of the input shaft 4 with the sun gear 3S being held immovable. As a result, the 3rd speed is set by the first planetary gear set 1 and the third planetary gear set 3 taking part in the transmission of the power, but the second planetary gear set takes no part. Unless the fourth clutch means K4 or the third brake means B3 is engaged, there is mechanically established the unconstrained chain, in which both the sun gear 2S and the carrier 2C are unconnected to other members including the casing 6. At the time of the shift from the 2nd to 3rd speeds, it is conceivable that the third brake means B3 is left engaged, namely, that the 3rd speed is set according to the pattern of column b. In case the 4th speed is to be set, the third brake means B3 has to be released, and the rotational speed of the sun gear 2S of the second planetary gear set 2, which has been held immovable by the third brake means B3, is increased to a value equal to that of the input shaft. In this case, the second planetary gear set 2 has to be brought into the unconstrained chain as the third brake means B3 is released. This likewise applies to the case in which the 3rd speed is to be set according to the pattern of column c so as to facilitate the shift from the 3rd speed to the 4th speed.
In connection with the planetary gear set thus brought into the unconstrained chain taking no part in the power transmission, the control of the revolving state of the rotary components of that planetary gear set can be executed by neither the control for setting the gear stages nor the control based upon the rotational speed of the input shaft 4 or the output shaft 5. Thus, the rotations may fluctuate highly or abruptly in accordance with the shift. As a result, shock accompanying the revolution fluctuations may possibly be felt as shift shocks when shifting into another speed stage in which the rotary components take part in power transmission.